Sofware: Digimarc
Digimarc gives you an ID to add them on your images that cannot be seen by the naked eye. You can only see the ID by using a graphic editing software like Adobe Photoshop (at least version 7.0) From the menu go to filters then Digimarc and read watermark. When you open a watermarked image, you can see a copyright icon at the upper left hand of the image. My ID is 896700 (I acquired it in year 1999) since I'm not using it anymore, I'm no longer belong to the Digimarc's database. You can't remove the ID by using 'save as', cut/crop, screen capture and obviously embed IDs. If you value or earn something from your works then Digimarc is for you.

Are there any flaws or holes?
Brilliant, You're thinking out of the box. It's 2007, you can reverse-engineer almost everything (but I will not allow anyone to reverse-engineer my works ). This deviation above is copyrighted and owned by Star Oriental oh by the way their Digimarc ID is 130061 (strange no longer working). Download this deviation now then read the watermark. Next download Star Oriental's
original image here >>> [link] again read the watermark. Did you see the difference? Same images but different IDs? Wait just a sec...I'm telling you right away that it is illegal to hack watermarked images, this is just a demonstration and for educational purposes only. Anyways today I'm going to 'steal' (haha jk!) err I mean I'm going add watermark on their images from our talented DA members like endintears, kynkyn, slumberdoll and blackmage9 Download all the images and read the watermark >>> [link] Done already? That is my ID: 896700.

Slumberdoll's Fictional Camera: Download properties.jpg or on windows see properties or with photoshop see file info>Section>EXIF(ctrl+5). Seems I'm playing too much